Formation of durable lubricous coatings have been found to be of great importance in the glass container industry to provide glass articles, or ware, with at least one layer of an adhering lubricating material in order to facilitate high speed automatic handling of glass articles in production lines, to protect articles against contact abrasion damage, and to prevent unsightly scuff and scratch damage. In this regard, uncoated glass articles are highly susceptible to abrasion damage, and it has been reported that newly formed uncoated glass articles can quickly lose up to 75% of their bursting strength due, at least in part, to surface abrasion caused by contact with other glass articles as normally occurs during processing and handling of such articles.
While some coatings have been applied to articles just prior to use, to be fully effective, the articles should be coated soon after they are formed, and in the case of annealed articles, for example, such coatings have been applied immediately before and/or after annealing.
In practice, pre-annealing coatings, sometimes referred to as "hot end" coatings, are applied to glassware after it leaves the glassware machine in an initial coater. The initial coater forms a very thin metal oxide coating on the outer surface of the glassware, which is then carried to the annealing lehr. Such pre-annealing coating methods and apparatus are disclosed, for example, in U.S. Pat. Nos. 4,431,692; 4,615,916; 4,668,268; 4,719,126; and 4,719,127 and others listed below.
A number of post-annealing coatings, sometimes referred to as "cold end" coatings, and methods and apparatus for their application, have been disclosed, for example, in U.S. Pat. Nos. 2,995,533; 3,386,855; 3,487,035; 3,712,829; 3,801,361; 3,876,410; 3,989,004; 3,997,693; 4,039,310; 4,130,407; 4,135,014; 4,517,242; 4,517,243; 4,529,657 and 4,812,332.
U.S. Pat. Nos. 3,876,410 and 3,989,004 disclose an apparatus and method for applying a coating material that is, at least in part, vaporizable at a readily obtainable temperature and capable of producing vapor that is contact-adherent to the article to be coated to produce a durable and tenacious, lubricous coating. In general, the patents disclose method and apparatus for forming acceptable coating material from organic materials, particularly hydrocarbons formed from methylene, ethylene, propylene, butylene, fatty acids and their derivatives and the like.
Caproic acid, stearic acid, oleic acid, myristic acid, linoleic acid and palmatoleic acid are disclosed as typical of the compositions yielding desirable coatings on glassware when used in the method and apparatus of these patents.
Oleic acid has been used in the commercial practice of the inventions of these patents. Oleic acid is a bland liquid in normal condition, having an appearance similar to that of cooking oil. It has been approved for use in connection with food products. As little as 1 drop of oleic acid every 17 seconds has been found sufficient to produce an acceptable lubricating coating on catsup bottles passing through the vapor at the rate of 80 bottles per minute. Thus, 1 drop of oleic acid provides sufficient vapor to coat about 20 catsup bottles. Further, oleic acid is readily available in high-grade quality at low cost. Because of these advantages, oleic acid has been a primary coating material used to provide post-annealing coatings.
The apparatus used to apply oleic acid in commercial practice includes a hood forming a vapor booth for a portion of a conveyer, which is operated to carry articles of glassware through the vapor booth. The vapor booth includes, generally, a booth top and an upper plate and a plurality of partitions between the booth top and the upper plate forming a plurality of plenum chambers arranged, one after the other, over and along the conveyer portion. The sides of the vapor booth are formed by a pair of downwardly extending panels that provide not only the means to support the vapor booth with respect to the conveyer, but a plurality of flow directing and controlling vanes in communication with each of the plurality of plenums. The upper plate of the vapor booth that forms the top of the plurality of plenums has a plurality of openings, one in each of the plurality of plenums, for carrying a fan in each of the plurality of plenums. The booth top also has a plurality of openings, at least one for each plenum, permitting vapor flow between the plurality of plenums and the booth formed by the booth top and sides. The upper plate carries a plurality of flow producing fans and fan motors, with one fan being located in each plenum, and the fans are capable of being rotated by their fan motors in alternatively opposite directions to provide counter-rotating flows of coating material vapor within the vapor booth and along the conveyer portion.
A plurality of vapor flows of oleic acid coating material are introduced through a plurality of vapor discharge tubes located to direct the flow of coating material vapor into the circulating flow of each plenum. The vapor of oleic acid coating material is formed by means forming a liquid coating reservoir including a bottom, four sides and a top. The oleic acid, which has a melting point of 57.degree. F. (14.degree. C.), is in a liquid state. The reservoir top also carries a vapor-forming nozzle having its liquid outlet connected with the coating material in the reservoir by an inlet tube extending from the vapor-forming nozzle to adjacent the reservoir bottom. The vapor-forming nozzle is also connected with a source of pressurized air for vaporization of the oleic acid coating material, and the vaporized coating material and pressurized air are directed from the vapor-forming nozzle through the reservoir top and into the reservoir, where the non-vaporous particles were removed by gravity. The remaining oleic acid vapor is urged by the influence of the pressurized air to and through the vapor discharge tube and introduced into the vapor hood for application to the glassware.
In practice, the oleic acid glassware coating is frequently supplemented by an additional cold-end coating using polyethylene to permit sterilization of the glassware. Oleic acid is liquid at temperatures in excess of 57.degree. F. (14.degree. C.). When glassware coated with oleic acid alone is exposed to elevated temperatures, such as in an autoclave for the sterilization of food containers, such as baby food jars, the oleic acid coating is substantially removed by the harsh and hot conditions, and the scratch resistance and lubricity are deleteriously affected, thereby increasing the risk of breakage. Breakage during processing is serious because of the possibility of slivers or fragments of the shattered glass being deposited in adjacent ware, which is completely unacceptable.